X-ray crystal structure studies will be undertaken on anticonvulsant drugs used in the treatment of grand and petit mal epilepsies, in order to establish relationships between biological activity and molecular structure. We have previously shown that the important anticonvulsants diphenylhydantoin and diazepam, although chemically unrelated, have striking conformational similarities. We have also determined the molecular structures of procyclidine and trihexyphenidyl, drugs with newly demonstrated anticonvulsant action, and shown that they contain these stereochemical features as well. It thus appears that the efficacies of these four agents against grand mal epilepsy are primarily due to the stereochemical components they have in common. Studies are currently in progress on other, chemically different, grand mal anticonvulsants, carbamazepine and ethyl phenacemide in order to see if they too possess conformational features similar to those shared by the above drugs. The structures of the anti-epileptic drugs primaclone (primidone) and phenurone will also be investigated by X-ray diffraction methods and their molecular structures compared in detail with the other anticonvulsants in order to correlate biological activity with molecular stereochemistry. Molecular structure studies will also be performed on agents used in the treatment of petit mal epilepsy. The drugs trimethadione and the ethosuximide, two chemically different but equally potent anti-petit mal drugs, will be structurally elucidated and their stereochemical features compared. Methsuximide and phensuximide will also be considered. We shall use the results obtained from these studies to initiate the syntheses of new anticonvulsant drugs, hopefully with more potency and less toxicity than the presently available agents.